The mitochondrion is the major source of energy in the eukaryotic cell, and an understanding of its functions and how they are controlled is of obvious importance. It is not at all clear why the mitochondrion contains an apparently autonomous protein-synthesizing system. An elucidation of the nature of this system and the products synthesized by it, however, will contribute to an eventual understanding of how the mitochondrion functions. Such an understanding is important also in determining the nature of the reported alterations in mitochondrial function during development of the animal from young to old and during the transition of normal cells to tumor cells. These studies are designed to determine the sequence of events and the factors involved in the three consecutive phases in mitochondrial protein synthesis at the ribosomal level: Initiation, polypeptide elongation, and polypeptide termination. A natural polysome system already isolated from mitochondria will be used. Studies will also be done on characterizing the products of mitochondrial protein syntheis.